Radio Frequency (RF) devices are quite popular in many ubiquitous applications such as Radio Frequency Identification (RFID) systems and remote sensing. For example, RFID systems consist of a number of radio frequency tags or transponders (RFID tags) and one or more radio frequency readers or interrogators (RFID readers). The RFID tags typically include an integrated circuit (IC) chip, such as a complementary metal oxide semiconductor (CMOS) chip, and an antenna connected thereto for allowing the RFID tag to communicate with an RFID reader over an air interface by way of RF signals. In a typical RFID system, one or more RFID readers query the RFID tags for information stored on them, which can be, for example, identification numbers, user written data, or sensed data. RFID systems have thus been applied in many application areas to track, monitor, and manage items as they move between physical locations.
More specifically, current RFID readers transmit information to RFID tags by generating and transmitting through the air continuous wave (CW) RF energy signals using an ON/OFF pattern as shown in FIG. 1. As seen in FIG. 1, that pattern has a frame repetition period that includes: (i) an ON portion wherein RF energy is amplitude, frequency or phase modulated for a defined time period (TON) at a maximum (as determined by FCC regulations) CW power level in order to transmit desired information to one or more RFID tags, and (ii) an OFF portion immediately following the ON portion wherein no RF energy is transmitted. In addition, as seen in FIG. 1, the initial ON portion of the RFID reader immediately follows a period wherein no RF energy is transmitted, and thus when transmitting information, current RFID readers are programmed and structured to transition from generating and transmitting no RF energy (i.e., a rest state) to generating and transmitting some predetermined maximum CW RF energy.
It has been discovered that in certain circumstances, transmitting CW RF energy in this manner causes interference with some critical care medical equipment. For example, it has been discovered that transmitting CW RF energy in this manner can cause interference with the heart pacing signals that are received by and the pacing outputs that are generated by a CRMD such a pacemaker or an implantable cardioverter defibrillator (ICD). Furthermore, RFID readers are not the only devices that output CW RF energy in this manner. CW RF energy in this manner is also output by, for example, RF transmitters/emitters of wireless communications systems such as cellular telephone systems.
Thus, there is a need for a method of controlling RF transmissions by RF emitters in RF transmission systems (such as an RFID system or a wireless communication system) in a manner that mitigates interference with critical care medical equipment, such as, without limitation, CRMDs, like pacemakers or ICDs.